Solved Z-offset keeps changing

It has to do with the standard operation of Z autoleveling using a probe.

The Z offset is actually a measure of where the nozzle is when the Z_min is triggered.

So what this means is that in a normal situation the probe would extend past the nozzle and make contact with the bed first, triggering a Z_min. The nozzle is now some distance in the air, say Z 1.0

In our application the nozzle acts as the probe and touches the bed first. The Z_min is detected after the nozzle contacts the bed and for all the software knows the nozzle is physically "In" the bed. In order to define the offset now you need to say it's Z -1.0

So in order to make it be further from bed (because you're too low) you need to make it more negative, since the nozzle is further "into" the bed than you're offsetting.

 

Glad tightening that up fixed it for you. I could tell in the video that is was spinning pretty bad. That is one of the main issues with the couplers. Also glad you got your offset fixed.

 

I have had the same problem and solved by cleaning Z rod. It had a tiny string of filament in its thread, which trapped between rod's and nut's threads every time, when the build plate raised closer to Z=0. It might sound like a minor thing to pay attention to, but it has randomly changed Z height slightly, causing failed prints.